KABUL, Afghanistan (AP) _ Hundreds of insurgents in a convoy of trucks attacked a police headquarters in southeastern Afghanistan, triggering a gunbattle Sunday that killed 22 people, officials said. It was one of the largest shows of anti-government force in over a year.

The fierce fighting in Paktika province was the latest in a wave of violence that has underscored just how unstable Afghanistan still is after U.S.-led forces toppled the Taliban in late 2001.

The assault began shortly before midnight Saturday when about 400 guerrillas traveling in trucks drove across the border from Pakistan and attacked the police headquarters in the province's Barmal district, about 200 kilometers (125 miles) southeast of Kabul, said provincial Gov. Mohammed Ali Jalali. It wasn't clear how he knew the men came from Pakistan.

Firing rockets, heavy machine guns and grenades, the attackers easily took over the office. About 15 to 20 Afghan police were in the compound at the time and seven of them _ including the district police chief _ were killed, Jalali said. The rest, realizing they could put up little resistance, fled.

Jalali said between 15 to 20 insurgents were also killed. Provincial police chief Daulat Khan said the attackers retreated with the bodies.

``These police died defending themselves,'' Jalali told The Associated Press from the provincial capital, Sharan. ``The attackers, they were a very big group.''

The insurgents held the police station until dawn Sunday before destroying the building, getting back in their vehicles and fleeing to Pakistan, eight kilometers (five miles) away, Jalali said.

It was unclear why the attackers retreated, but Jalali said they likely did so because by daylight, word of the attack would have been passed on to the U.S.-led coalition, against which they would be little match.

Coalition forces have massive air power at their disposal and routinely use it when insurgent positions are identified.

Previous battles between insurgents and government forces backed by the U.S.-led coalition have rarely involved more than 80 guerrilla fighters. Anti-government forces usually move around in small groups on foot.

``For a large number of people in vehicles to cross the border in daylight requires some guts as well as some coordination,'' a senior government official said on condition of anonymity.

He said the issue would be discussed when Pakistani Foreign Minister Khursheed Kasuri visits Kabul on Thursday, and Afghan authorities would press Pakistan to do more to police its side of the border.

Jalali said the insurgents responsible for Sunday's attack included Taliban and fighters loyal to Gulbuddin Hekmatyar, a former prime minister who heads Hezb-e-Islami, a faction which has called for attacks against foreigners in Afghanistan. He also blamed Pakistan's intelligence service for playing a role in organizing the assault.

Pakistan abandoned its support for the Taliban following the Sept. 11, 2001 attacks in the United States. The nation has since become a key ally of the United States in its war on terror, arresting more than 500 suspected al-Qaida operatives.

However, the deeply conservative tribal belt that runs along Pakistan's border with Afghanistan is believed to be a safe haven for fleeing Taliban, who share both ethnic and religious links to Pakistani tribesmen.

Thousands of Pakistani soldiers have been deployed along the porous and rugged border. But tribesmen in the area openly say they would protect fleeing Taliban.

Sunday's assault came just days after 64 people were killed Wednesday in various attacks around the country. The violence included a bus bombing that killed 15 and a battle between feuding warlords, both of whom were loyal to the Afghan government.

The top U.N. envoy for Afghanistan, Lakhdar Brahimi, has asked the Security Council to expand the 5,000-strong NATO-led peacekeeping force to ensure security outside the capital ahead of national elections due in June 2004.

The government wants to disarm militias scattered around the country, but U.N. disarmament adviser Sultan Aziz said Sunday the long-delayed campaign might not get started for another six weeks, partly because the Defense Ministry has been slow to make crucial reforms that must come first.

Critics say a small clique of ethnic Tajiks, led by Defense Minister Mohammed Fahim, are reluctant to give up a virtual stranglehold on the Defense Ministry _ a prize that fell into their hands after U.S.-led forces ousted the Taliban in 2001. The group fears that any changes would reduce Fahim's power.

One of the keys to Afghanistan restoring stability is believed to be the strengthening of its national army, which now numbers just 5,000 soldiers. The government wants it to have 70,000 troops over the next several years.

U.N. spokesman David Singh said Sunday that the army opened its first recruiting center in the east of the country. Other recruiting centers are due to open in at least five other regions, Singh said.

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AP writer Amir Shah in Kabul contributed to this report.